Let’s start by explaining that semen, or the ejaculate, is the exciting stuff you know about after ejaculation. Semen is made by the prostate gland and seminal vesicle glands under the bladder.
Sperm, on the other hand, are produced by the testicles but contribute only 2% of the volume of semen. The purpose of sperm is to fertilise an egg, whilst semen nourishes and provides a transport medium for the sperm.
There are two Vas Deferens, or tubes, each carrying sperm from the testicles to the ejaculatory ducts under the bladder where the sperm mixes with semen. Vasectomy is a minor surgical procedure that blocks each vas deferens about two thirds of the way from the upper pole of the testicle to the base of the penis. Sperm is therefore prevented from getting into semen, and are absorbed back into the body.
Success is confirmed with a semen test approximately 25 ejaculations and 12-14 week later when the semen is clear of sperm. Sex and ejaculation feel the same but pregnancy is prevented. The chance of a pregnancy ever occurring after a negative post vasectomy test is exceptionally low at 1 in 2,000.